Ultra high molecular weight polyethylene (UHMWPE) is presently the plastic material most commonly used in orthopaedic prostheses. Wear of this material in load-bearing components (e.g., knee and hip replacements) is a serious problem which limits the lifetime of the prosthetic devices. Spire Corporation proposes to study the use of ion implantation to improve the wear performance of UHMWPE, High energy ions of helium, titanium, and fluorine will be implanted into UHMWPE samples, some of the Ti samples will also be oxygen-implanted. All of the ion implantation species are expected to increase the surface hardness and thus the wear resistance of the UHMWPE. without affecting crucial bulk properties. The materials formed in the ion implanted layer are known to be biocompatible. During the proposed program, samples of UHMWPE will ion implanted, and measurements of surface hardness, coefficient of friction, and wear resistance will be compared with these of unimplanted control samples. A successful demonstration of improved wear resistance of UHMWPE would lead to a Phase II program in which ion implantation parameters are optimized, detailed analysis of the effects of ion implantation would be performed, and initial step toward commercialization would be made.